1. Field of the Invention
The invention relates to a proposal for an improved handling of fluid hydrocarbon mixtures having a tendency forming solid organic deposits, especially based on hydrocarbons, upon storage and/or when processed, which deposits then will remain as undesired incrustations in the interior of pipelines, pumps, filters, containers and the like and require a considerable expenditure for cleaning. Particularly concerned by this problem are the areas of extracting, storing and/or conveying crude oils having high contents of paraffinic hydrocarbons and/or of correspondingly handling oil fractions containing such hydrocarbon compounds. Nevertheless, comparable problems may also arise in extracting and processing natural gas; hereto cf., for example, F. Kerekes et al., xe2x80x9cMaxcex2nahmen gegen Paraffin-Ablagerungen in der Erdxc3x6l- und Erdgasfxc3x6rderungxe2x80x9d, Erdxc3x6l-Erdgas-Zeitschrift 99 (4/1983), 110-118 and the literature quoted therein.
Functional disorders caused by a deposition of proportions of organic solidsxe2x80x94and more particularly paraffins and/or asphaltenesxe2x80x94contained in hydrocarbon mixtures that are fluid under normal conditions are various in nature and, thus, become manifest in a great variety of ways. One important parameter in this respect is the temperature range of the pour point or of the setting point of the liquid hydrocarbon mixture. In the temperature range exceeding this value, the fluidity would be basically ensured, while the hydrocarbon mixture will solidify at temperatures below said value. Crude oils and/or hydrocarbon fractions having comparably high pour and setting points may be improved with respect to the flow property thereof also at reduced temperatures by the addition of so-called Pour Point Depressants (PPD""s). The addition of PPD""s, due to an interaction with the amounts of solids crystallizing in the liquid phase, reduces the limiting temperature below which the fluidity of the hydrocarbon mixture is lost.
However, independently of the problem area referred to herein, there exists a complex second problem area for the practical handling of such liquid hydrocarbon mixtures, but also of gaseous hydrocarbon mixtures. This is related to the incrustations which in practice give rise to a variety of disorders and have been formed by solid hydrocarbon compounds on the inner walls of, for example, pipelines, pumps, on filters or in storage tanks, which incrustations occur even if the fluidity of the hydrocarbon mixture itself is retained. Thus, for example, the interior of pipelines for the transportation of crude oil must be regularly subjected to cleaning procedures which are expensive in time and costs, because in the regular operation of conveying oil incrustations of solid hydrocarbon compounds are increasingly formed on the inner wall of the pipelines. The working order of pumps and filters is threatened by such formation of incrustations during the continuous operation, if incrustations of this type are uninhibitedly permitted to build up. Particular threats in thus directions are caused also by that the normally flowing liquid hydrocarbon-based material is intermittently exposed to inevitable standstill periods.
2. Discussion of Related Art
Hitherto the efforts made in the art for finding solutions to these problems have had only a restricted practical success. What has been desired is, by adding efficient inhibitors to prevent, or at least to reduce, this undesirable tendency towards incrustation and more particularly the strong adhesion of the, e.g., paraffinic incrustations to the solid surfaces being in contact with the liquid and/or gas phases. Here, the addition of the known PPD""s lowering the setting and/or pour point(s) of the kind discussed above does not provide remedy. Really useful inhibitors for the goal according to the invention so far have not been proposed in connection with liquid hydrocarbon mixtures. The literature reference quoted above from Erdxc3x6l-Erdgas-Zeitschrift 99 deals with paraffin deposits from natural gas condensates, among others. Here, laboratory experiments were reported for developing paraffin inhibitors based on wetting agents and/or dispersants. Such wetting agents acting through a water phase form a surface film on the walls which largely counteracts a deposition of paraffins and/or infiltrates and mobilizes films already present, respectively. More specifically, for practical use there is proposed a combination of a nonylphenol ethoxylate and a dodecylbenzyl sulfonate.
The teaching according to the invention is based on the recognition that two substance classes preferably having a surfactant character as described in detail hereinbelow are capable of providing remedy to the problems concerned here in a hitherto unknown manner. These auxiliary agents of the invention, hereinbelow designated as the active substances (A) and (B), are obviously distinguished by that they are capable of striking and spreading on the solid work material surfacesxe2x80x94conventionally metal surfacesxe2x80x94and here counteract the attachment and growth of solid hydrocarbon deposits and, hence, the undesirable incrustation, supposedly so due to the chemical nature thereof.
Thus, the invention relates to the use of
(A) esters of phosphoric acid and/or partial salts thereof with alkoxylated aliphatic, cycloaliphatic and/or aromatic alcohols and/or
(B) fatty acid oligo-dialkanolamides
as inhibitors against the formation of solid hydrocarbon incrustations from hydrocarbon mixtures which are fluid and prone to form such incrustations. The term xe2x80x9caromatic alcoholsxe2x80x9d as used in the context of the component (A) includes phenols and corresponding compounds having the OH group(s) bonding to the aromatic moiety.
It is preferred to employ inhibitors according,to (A) and/or (B) which exhibit surfactant character and, in addition, are capable of-wet,tig solid work material surfaces and especially of spreading on solid work material surfaces also in the presence of the fluid hydrocarbon phase, even if this is comprised by liquid hydrocarbon mixtures. The inhibitors of the invention according to (A) and/or (B) are especially suitable for the protection of metallic work material surfaces which are in contact with the fluid hydrocarbon phase tending to form incrustations.
Re the definition of the inhibitors (A) according to the invention:
The active substances of this class of inhibitors used according to the invention are esters of phosphoric acid with selected alcohols. Included in the invention is the use of the phosphoric acid triesters. In preferred embodiments there are employed partial esters or mixtures of partial esters of phosphoric acid and the selected alcohols still to be described herein-below. In the case that such partial esters are used, it may be expedient to utilize the non-esterified acid groups in the form of salts thereof, and especially in the form of alkali metal salts, ammonium salts, alkanolamine salts and/or amine salts. As the inhibitor component (A) there may be particularly suitable mixtures of mono- and/or diesters of phosphoric acids and/or their respective salts.
Within the scope of this inhibitor component (A) there are employed, as the ester-forming alcohol components, alkoxylated aliphatic, cycloaliphatic and/or aromatic alcohols which preferably contain at least 3, especially at least 4 to 6, carbon atoms in the aliphatic, cycloaliphatic and/or aromatic alcohol moiety. A particularly suitable class of ester-forming alcohols is constituted by alkoxylated phenol- derivatives, among which alkoxylated alkylphenols may be of particular importance as phosphoric acid ester-forming alcohol components. Alkoxylated fatty alcohols constitute a further preferred class of compounds for composing the inhibitors (A).
As the alkoxylated products of said alcohols within the scope of the invention there are especially utilized the ethoxylated and/or propoxylated derivatives of monofunctional alcohols or phenols, respectively. The degree of alkoxylation may be, for example, within the range of from 1 to 20, and especially within the range of from about 3 to 15, and is in detail in a per se known manner also dependent on the size of the respective hydrocarbyl moiety in the monofunctional alcohol. Thus, e.g., ethoxylated nonylphenols having an average of 5 to 10 ethylene oxide (EO) units per 1 mole of nonylphenol have proven to be very suitable as balanced and efficient alkoxylated alcohols for the formation of the inhibitor component (A) within the scope of the invention. One preferred component (A) for the teaching according to the invention comprises mixtures of the sodium salts of mono- and diesters of phosphoric acid with such nonylphenol/5-10 EO adducts. EO adducts of fatty alcohols of the range of C8-20, and especially C10-18, comprising from 1 to 20 EO units, and preferably about from 3 to 15 EO units, are a further important class for the formation of the inhibitors under (A).
The inhibitors used according to the invention of the active substance class (B) are fatty acid oligo-dialkanolamides. Within this meaning, the term fatty acid includes monocarboxylic acids containing at least 6 to 8 carbon atoms, while acids containing at least 10 carbon atoms and above all monocarboxylic acids of the range containing 12 and more carbon atoms are especially preferred. The carboxylic acid, in consideration of the explanations further provided hereinbelow, may be saturated and/or unsaturated. Olefinically mono- and/or polyunsaturated carboxylic acids, particularly from the range of C12-24, are particularly suitable representatives.
In the inhibitor component (B) according to the invention the carboxylic acids are present as oligo-dialkanolamides, i.e. as carboxylic acid amides from the reaction with a limited excess of dialkanolamines. Preferred as the dialkanolamines are compounds having comparably low hydroxyalkyl moieties, especially with corresponding moieties having up to 5, and preferably up to 3, carbon atoms. Diethanolamine may be especially suitable for the preparation of the inhibitor component (B).
Suitable to serve the purpose according to the invention are reaction products of fatty acids prepared by using a slight excess of the dialkanolamine over the amount stoichiometrically required for the formation of the fatty acid amide. Especially suitable are inhibitor components (B), in the preparation of which the fatty acid-based reaction component has been reacted with an at least about 0.5 molar excess of the dialkanolamine. Suitable may be reaction products of fatty acids and dialkanolamines which comprise the dialkanolamine in an about 0.5 to 3.0 molar excess, relative to the amount of carboxylic acid. If the reaction of the reactants forming the inhibitor component (B) is carried out at sufficiently high temperaturesxe2x80x94for example at temperatures in excess of 175xc2x0 C. to 180xc2x0 C.xe2x80x94then the formation of the carboxylic acid amide proceeds, on the one hand, while, on the other hand, an extension of the chain of the amide-forming reactant is effected due to a removal of water and an ether formation between the free hydroxyl groups of the dialkanolamines, as is shown hereinbelow for an idealized reaction between one mole of a carboxylic acid RCOOH and two moles of diethanolamine:
At reaction temperatures in the range of about 190xc2x0 C. a fatty acid amide having the idealized formula 
is obtained. Possible is also a linkage with the formation of a tertiary N atom in the chain-extended group.
For the effect provided by the inhibitor component(s) (A) and/or (B) according to the invention it can be important that they have some fluidity. In this respect, more particularly, in the selection of the carboxylic acid amide compounds, olefinically mono- and/or polyunsaturated carboxylic acids may be of importance. The respective fatty acids of natural origin, and among these especially olefinically unsaturated fatty acid mixtures are particularly suitable for the preparation of the inhibitor-components (B). Known as one significant example for this are tall oil fatty acids a by far predominant proportion of which consists of a mixture of olefinically monounsaturated, di-unsaturated and tri-unsaturated C18-monocarboxylic acids. Other suitable natural feed materials for unsaturated fatty acids are vegetable ester oils comprising olefinically monounsaturated and, as the case may be, polyunsaturated carboxylic acids, especially those of the range of C16-24. For example, palm oil, peanut oil, castor oil soybean oil, fish oil and especially rapeseed oil may be mentioned here.
Each of the inhibitor components (A) and (B) as defined according to the invention may be put into use alone by itself in the hydrocarbon mixture susceptible of forming incrustations. However, it is preferred to use mixtures of (A) and (B), where the broad range of ratios of amounts of A/B of from about 5/95 to 95/5 is contemplated. Preferred mixing ratios are within the range of from about 25/75 to 75/25 and more particularly those within the range of from about 40/60 to 60/40. The ratios of amounts and/or ranges, respectively, are based on the ratio by weight of the components (A) and (B). Particularly equal inhibitor mixtures under the teaching of the invention contain approximately equal amounts by weight of (A) and (B).
A number of technical options exists for rendering the wall areas intended to be protected inert to the undesired build-up of incrustations. One embodiment comprises applying the inhibitors or inhibitor mixtures in a suitable auxiliary liquid onto the wall areas to be protected and allowing them to be adsorbed thereon. For example, solutions of the inhibitors or inhibitor mixtures, respectively, in solvents can be applied onto the wall areas to be protected, for example by spraying, before the respective working device will be contacted with the hydrocarbon mixture susceptible of forming incrustations.
Suitable as auxiliary liquids, more particularly, are appropriate aqueous and/or organic systems. The inhibitors used according to the invention, in the preferred embodiment, possess some dissolving power and/or self-emulsifying power in an aqueous phase, due to their surfactant character, and in this form may be conveyed to the wall areas to be protected or to other solid areas. However, solutions and/or emulsions of the inhibitors in organic or organic-aqueous liquid systems are also suitable for use in such a pretreatment, due to the high affinity to solid surfaces, more particularly those made of metal. If required, the homogeneity of the liquid phase for rendering the wall areas intended to be protected inert to the undesired build-up of incrustations can be ensured by using auxiliary emulsifiers in a per se known manner.
Nevertheless, the formation of the protective layers according to the invention against the undesirable formation of incrustations is not restricted to such pre-treatment of the regions to be protected. It is much easier, as a rule, to add comparably low amounts of the inhibitors to the hydrocarbon mixtures which, in the absence of the additives according to the invention, cause the undesired formation of the incrustations to take place. Thus, it may be appropriate to add the surfactant inhibitors to liquid hydrocarbon mixtures in amounts of about from 5 to 1,000 ppm, preferably in amounts of about from 10 to 500 ppm and especially in amounts of about from 20 to 200 ppm. It has been shown that even in such high application dilutionsxe2x80x94which in practical use may range from about 30 to 100 ppmxe2x80x94the surface-active inhibitors are adsorbed on the wall areas made, for example, of metal, and here efficiently attain the object according to the invention. Moreover, it has been shown that an efficient protection can also be achieved, if this addition of the inhibitors according to the invention is effected just batchwise, for example as an additive to a crude oil stream passed through a pipeline. The interior wall areas remain inert to an undesirable paraffin deposition over a considerable period of time, even if in this subsequent period the crude oil stream does not contain any inhibitor components. The embodiments described here may also be combined.
In an important embodiment of the invention, the inhibitor components (A) and (B) as defined are used in combination with conventional setting point depressants, with respect to the nature of which reference may be made to pertinent prior art. Commercial setting point depressants are known to be, for example, branched polymer compounds having some longer residues, for example acrylate polymers comprising moieties of long-chain fatty alcoholsxe2x80x94especially those of the range C20-24xe2x80x94in an ester bond to the polymer chain. Further examples of known flow improvers or setting point depressants of the kind referred to here are to be assigned to the classes of the polyethylenes and the ethylene-vinyl acetate copolymers add/or ethylene-vinyl propionate copolymers. Even if the detailed mechanism of action of these products has not been fully elucidated, they have in common that first the modifying auxiliary agents will have to be heated together with the crude oil at temperatures much above the setting point. Upon subsequent cooling, interactions occur between the dissolved inhibitors of the PPD type and the precipitating organic solids. Normally, the crystal growth will he hindered, so that small particles are formed which do not permit a formation of networks. As for details, reference is made to the publication as initially quoted in Erdxc3x6l-Erdxc3x6l-Erdgas-Zeitschrift 99, 113-114.
The inhibition of the incrustation within the scope of the teaching of the invention obviously is governed by different principles. Adsorption onto the wall surfaces to be protected from an incrustation build-up and spreading on said wall surfaces of the inhibitors (A) and/or (B) according to the invention does not require the combination of flow components to be heated, for example of the crude oil stream to be conveyed and inhibitors or inhibitor combination, respectively.
However, it was found that the concomitant use of the inhibitors (A) and (B) according to the invention may also exert an influence on the manifestation, for example, of the paraffinic solid crystals being formed in the oil stream. Crystal formations like those formed below the so-called cloud point may also be affected by the concomitant use of the inhibitors (A) and (B) according to the invention. Investigations have shown that a characteristic phenomenon may be represented by a reduction in size of the crystallites and, thus, the solids particles being in solid communication with each other. This phenomenon may give a positive effect onto the flow behavior of the oil stream containing solid precipitates, even if this would not necessarily involve a decrease in the setting point.